Word wrap kata in Python

wordwrap.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import unittest

def wrap(s, w):

  def split(s, at, gap=0):
    return s[:at] + '\n' + wrap(s[at + gap:], w)

  if w <= 0 or len(s) <= w:
    return s
  p = s.rfind(' ', 0, w + 1)
  # refactoring... refactoring...
  return split(s, at=p, gap=1) if p >= 0 else split(s, at=w)


class testWrap(unittest.TestCase):

  def test_wrap(self):
    # degenerate case
    self.assertEqual('', wrap('', 1))
    # check for zero length
    self.assertEqual('1', wrap('1', 0))
    # s fits in w
    self.assertEqual('1', wrap('1', 1))
    # s still fits in w
    self.assertEqual('1 2', wrap('1 2', 3))
    # s no longer fits in w, but has space before w
    self.assertEqual('1\n23', wrap('1 23', 3))
    # s has space at w
    self.assertEqual('12\n3', wrap('12 3', 3))
    # s has more than one space
    self.assertEqual('12\n3 4', wrap('12 3 4', 3))
    self.assertEqual('1 2\n3 4', wrap('1 2 3 4', 3))
    # s is long enough to wrap twice: at w...
    self.assertEqual('123\n456\n7', wrap('123 456 7', 3))
    self.assertEqual('1 2\n3 4\n5', wrap('1 2 3 4 5', 3))
    # ... and before w...
    self.assertEqual('12\n34\n567', wrap('12 34 567', 3))
    self.assertEqual('1\n23\n456\n7', wrap('1 23 456 7', 3))

    # s no longer fits in w, but has no space either
    self.assertEqual('123\n4', wrap('1234', 3))


if __name__ == '__main__':
  unittest.main()